Summary: Ref T4398. Prevent users from brute forcing multi-factor auth by rate limiting attempts. This slightly refines the rate limiting to allow callers to check for a rate limit without adding points, and gives users credit for successfully completing an auth workflow. Test Plan: Tried to enter hisec with bad credentials 11 times in a row, got rate limited. Reviewers: btrahan Reviewed By: btrahan Subscribers: epriestley Maniphest Tasks: T4398 Differential Revision: https://secure.phabricator.com/D8911